1. Field of the Invention
This invention relates to oriented synthetic crystal assemblies and more particularly to an assembly of synthetic crystals of diamond, or like materials, positioned together and oriented so as to provide the assembly with enhanced physical properties, and to a method and apparatus for making the assembly.
2. Description of the Related Art
Diamond crystals have numerous physical properties that are well known and which have great utility for industrial purposes but which in the past have not been fully exploited. These properties include abrasion resistance, thermal conductivity, electrical insulation, and receptivity to the deposit of a layer of diamonds by chemical vapor deposition.
More specifically, it has long been known that diamond crystals have a very high degree of abrasion resistance and that this resistance varies with the crystallographic direction of abrasion by a factor of as much as about one hundred times. This most resistant direction is along the diagonal of a cubic face in the plane of the face. (See Denning, R. M. "Directional Grinding Hardness in Diamond," American Mineralogist, (1953) 38, 108-117.)
Furthermore, the thermal conductivity of diamond reaches a value of up to five times that of metallic copper. (See Wilks, J. and Wilks, E. Properties and Applications of Diamond, Butterworth-Heinmann Ltd., Oxford (1981), 166 and 512.)
The electrical properties of diamond useful in semiconductor applications have been recognized by Wilks, J. et al., op. cit., p. 63 and others, e.g., the Geis et al. PCT application WO 92/01827 published 6 Feb. 1992, and Geis et al. "Large-Area Mosaic Films Approaching Single-Crystal Quality," Applied Physical Letters, Vol. 58, No. 22 (3 Jun. 1991), 2485-2487.
Still further, it is known that diamond can be deposited as a layer by chemical vapor deposition onto a crystal of diamond and retain the crystallographic orientation of the diamond substrate with an epitaxial relationship. (See Wilks, J. et al., op. cit., p. 20 et seq.)
Notwithstanding the knowledge of these properties over many years, the prior art has failed to recognize how to take full advantage of them. Wilks, J. et al., op. cit., pp.17-20, records that large blocks of polycrystalline diamonds, known as PCD, have been produced by sintering together a mass of fine diamond crystallites in randomly oriented manner to minimize cleavage and thus improve strength and hardness, but such random orientation of the crystallographic directions of the crystals does not optimize the property of abrasion resistance in the block as a whole that is inherent in an individual diamond crystal.
Again, the sintering or binding material in a block of PCD occupies a substantial proportion of the volume of the block and is of a much lower thermal conductivity than diamond. As a result, the thermal conductivity of the block is much lower than could be achieved with a pure or more nearly pure block of diamond. Also, the sintering material is typically metallic and is a good electrical conductor, whereas diamond is known for its electrical insulating properties. Thus, blocks of PCD do not take advantage of the electrically insulating properties of diamond.
Still further, the random orientation of such sintered fragments or crystals in PCD does not permit chemical vapor deposition of a layer of a single crystal of diamond on a surface of a block of PCD.
More recently, the cited Geis et al. references recognize that diamond's excellent electrical properties have not been fully utilized in semiconductor devices. These references teach the placing of synthetic diamond seed crystals of 0.10 mm diameter or less in spaced complementary pits or grooves, and subsequently growing a film about the seeds by chemical vapor deposition. Geis et al. intentionally separate the seed crystals to enable the CVD crystal growth to envelope the seeds. Thus, although Geis et al. state that such placement orients the crystallographic directions, their method creates spaces or gaps between adjacent seed crystals. Thus, they state that at the point where adjacent crystals merge, there is the possibility that crystal defects may occur. Moreover, Geis et al. is concerned with electrical applications and thus does not teach how to produce a bearing surface having a crystallographic direction of maximum abrasive resistance.
In understanding the problems with the prior art and the solutions realized by the present invention, it is important to recognize that diamond crystals have long been synthesized in several shapes. Diamond crystals in shapes ranging from cubic to cubo-octahedral to octahedron shapes have thus been synthesized for many years and are commercially available. By regulating the temperature, pressure, and chemical environment of synthesis, it is possible to synthesize cubic or predominantly cubic diamond crystals. (See Litv, Y. A. and Butuzov, V. P. "Growth of Synthetic Diamond Crystals," Soviet Physics-Duklody Vol. 13, No. 8 (February 1969), 746, 747 or Wilks, J. et al., op. cit., p. 127.) Also, it is noted that such crystals in sizes approximating 1 mm have been commercially available for many years (Wilks, J. et al., op. cit., p. 14).